Sunday, August 5, 2007

In this post, I examined why defensive performance has a higher correlation with playoff success and determined that the root was the greater abundance of very good offenses among playoff teams. Thus, teams needed better defenses to make it through the playoffs. It's not a matter of one unit being more important than the other. It's a matter of balance. In this article, I redid the previous experiment using Football Outsiders' DVOA stats instead of my own VOLA stats. DVOA covers the same time period as the original experiment: 1996-2006. It's very important to point out that my VOLA statistics covered only the regular season, but the DVOA stats used here are based on regular season and postseason (where applicable) performance. This probably biases certain stats used here, such as the average DVOAs of Super Bowl winners, simply because the DVOAs used take into account that the teams performed well against good teams in the postseason, which isn't necessarily indicative of their regular season performance (see the 2006 Colts). The results, however, support what I said the last time.

For the following tables, O=Offense, D=Defense, R=Run, P=Pass, ST=Special Teams.

The correlation coefficients with the seeds are actually the correlation coefficients with 7-(Seed #), where the seed # is 7 for non-playoff teams. So the second column includes all teams (where the seed input is between 0 and 7), but the third column includes only playoff teams (where the seed input is between 1 and 7).

Corr To Wins

Corr to Seed (all teams)

Corr to Seed (playoff teams only)

O

0.6478

0.49578

0.19407

RO

0.4697

0.35797

0.23226

PO

0.6241

0.47916

0.11531

D

-0.5252

-0.3899

-0.27018

RD

-0.3517

-0.25361

-0.202

PD

-0.5066

-0.37634

-0.25634

ST

0.2603

0.23787

0.18571

For this table, defensive DVOAs less than or equal to -X% are tallied in the ≥X% columns.

ALL TEAMS

≥10 (Teams)

≥10 (%)

% Made Playoffs

≥20 (Teams)

≥20 (%)

% Made Playoffs

O

68

19.825

79.412

21

6.1224

90.476

RO

45

13.12

66.667

11

3.207

63.636

PO

101

29.446

73.267

49

14.286

85.714

D

77

22.449

68.831

17

4.9563

82.353

RD

97

28.28

53.608

21

6.1224

47.619

PD

95

27.697

61.053

34

9.9125

70.588

ST

1

0.29155

0

0

0

0

PLAYOFF TEAMS

Median

Mean

O

6.65

7.475

RO

1.55

1.1735

PO

11.85

13.123

D

-7.15

-6.903

RD

-7.9

-7.0205

PD

-8.55

-6.8765

ST

0.95

0.97121

SB WINNERS

Median

Mean

O

11.5

12.582

RO

6

3.9273

PO

17.8

20.936

D

-15.1

-14.155

RD

-12

-10.955

PD

-14.9

-17.373

ST

2.2

2.3455

Teams with very good offenses are more common than teams with very good defenses, and teams with very good offenses are more likely to reach the postseason than teams with very good defenses. Having either still gives you a pretty good chance of making the playoffs. Having both makes it nearly certain. 28 out of 30 teams (93.33%) that had at least a 6% Off. DVOA and at least a -6% Def. DVOA made the playoffs. The only 2 teams not to were the 2002 Miami Dolphins, who blew a big lead late in the final game of the season against the Pats, and the 1999 Oakland Raiders, who were #3 in total DVOA but posted an 8-8 record.

Defense, however, has the higher correlation with playoff seeding. When nearly 70% of playoff games are won by the home team, seeding becomes very important. Then again, a higher seeding usually indicates a better team. Looking at the DVOAs, the home team is the better team in about 67% of postseason games, and the home team wins 69% of postseason games. The home teams win 70% of games in which they are better and 60.6% of games in which they are worse (though this number has dropped to 40% since the realignment in 2002).

On average, the Super Bowl winner is a balanced team. The offense DVOA is above 10%, and the defense DVOA is below -10%. And actually, the average defense DVOA comes out slightly higher. Special teams DVOA is positive as well. The worst offensive DVOA of a Super Bowl winner belongs to the 2000 Ravens (-7%), and the worse defensive DVOA belongs to the 2006 Colts (11%). The Ravens, however, at least had a good running game (8.3%). In 11 Super Bowls, the team with the better total DVOA won 9 times. The two exceptions were the 2001 Patriots and the 2006 Colts. The 2006 Colts, however, had the better weighted DVOA, in which the latest games are weighted more strongly. Seven champions had better offensive DVOA, and seven champions had better defensive DVOA. Six champions had better special teams DVOA. Four had better offensive and defensive DVOA. Only 2 champions were better in all three categories. All of the champions were better in at least one category (2001 Patriots had better ST DVOA than the Rams).

People often point out the Ravens and the Bucs to say that defense wins championships. While Baltimore won in 2000 with a -7% offensive DVOA, they had a better total DVOA than the Giants, who had a good defense (-8.2%) but a weak offense (4.4%) compared to the Ravens' monstrous -30% defensive DVOA. The Ravens also had better special teams (7.2% vs -4.4%). Similarly, the Bucs had better special teams and defense, which was historically good. The Raiders' offense, which was damned good (24.4%) couldn't hold up, but it's hard to quantify the impact of Barrett Robbins and Jon Gruden's vast insider knowledge. The first paragraph of the game summary section of Super Bowl XXXVII's Wikipedia entry indicates that the Raiders' offense was at a huge disadvantage because of Gruden's knowledge. So you can win with a mediocre offense (4 out of 11 had <1% DVOA), but it's reliant on the matchup (the Raiders, the 2003 Patriots' 0.4% Off. DVOA and the Panthers' -7.2% Off. DVOA) and you probably need a ridiculously good defense. Only two teams, however, have won with a mediocre defense (>0% DVOA). The 1998 Broncos had a really good offense led by John Elway and Terrell Davis (28% DVOA), and the 2006 Colts had a really good offense. The Broncos played a well-balanced Falcons unit (10.1% Off, -13.4% Def, 2.8% ST), too.

Teams like the '00 Ravens and '02 Bucs have struggled since their Super Bowl wins because defensive performance is less consistent on a yearly basis, and they did not have the capability on offense to make up for the performance loss. The Colts will struggle to duplicate their success in '06 as well without at least an average defense.

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About the Author

My degree is in computer science, and the football research started as an independent study in artificial neural networks. As a lifelong NFL fan, I wanted to explore the relative importance of different factors in winning games. Since the research is still nascent, I wanted to put it out in the public domain and hopefully find others interested in teaming up. Once it becomes profitable, though... I just hope the mafia families running Vegas don't come to hurt me.